Liquid crystal display device comprises a liquid crystal cell and polarizing plates. The polarizing plate usually has protective films and a polarizing film, and is obtained typically by dying the polarizing film composed of a polyvinyl alcohol film with iodine, stretching, and being stacked on both surfaces thereof with the protective films. A transmissive liquid crystal display device usually comprises polarizing plates on both sides of the liquid crystal cell, and occasionally comprises one or more optical compensation films. A reflective liquid crystal display device usually comprises a reflector plate, the liquid crystal cell, one or more optical compensation films, and a polarizing plate in this order. The liquid crystal cell comprises liquid-crystalline molecules, two substrates encapsulating the liquid-crystalline molecules, and electrode layers applying voltage to the liquid-crystalline molecules. The liquid crystal cell switches ON and OFF displays depending on variation in orientation state of the liquid-crystalline molecules, and is applicable both to transmission type and reflective type, of which display modes ever proposed include TN (twisted nematic), IPS (in-plane switching), OCB (optically compensatory bend) and VA (vertically aligned), and ECB (electrically controlled birefringence).
Of these LCDs, most widely used for application in need of high definition display is 90° twisted nematic liquid crystal display (referred to as “TN mode”, hereinafter) using nematic liquid crystal molecules having a positive dielectric anisotropy, driven by thin-film transistors. The TN mode has viewing angle characteristics such as ensuring excellent display characteristics in the front view, but as being degraded in the display characteristics in an oblique view, such as causing lowered contrast, or grayscale inversion which is inversion of brightness in a grayscale image, which are strongly desired to be improved.
In recent years, there has been proposed a vertically-aligned nematic liquid crystal display device (referred to as “VA mode”, hereinafter) as a mode of LCD capable of improving the viewing angle characteristics, in which nematic liquid crystal molecules having a negative dielectric anisotropy is used, wherein the liquid crystal molecules are oriented so as to direct the long axes thereof nearly normal to the substrate under no applied voltage, and are driven by thin-film transistors (see Japanese Laid-Open Patent Publication “Tokkai” No. hei 2-176625). The VA mode is not only excellent in the display characteristics in the front view similarly to the TN mode, but can exhibit wider viewing angle characteristics through adoption of a retardation film for viewing angle compensation. The VA mode is successful in obtaining wider viewing angle characteristics by using two negative uniaxial retardation films, having the optical axes normal to the film surface, on the upper and lower sides of a liquid crystal cell, and it is also known that further more wider viewing angle characteristics can be obtained by additionally applying an uniaxial orientation retardation film having an in-plane retardation value of 50 nm and a positive refractive index anisotropy (see SID 97 DIGEST, p. 845-848).
Use of two retardation films (SID 97 DIGEST, p. 845-848), however, results not only in increase in the cost, but also in degradation in the yield ratio due to need of bonding a number of films, wherein use of a plurality of films raises a problem of increase in the thickness, which is disadvantageous for thinning of the device. An adhesive layer used for stacking stretched films may shrink under varied temperature and humidity, and may cause failures such as separation or warping of the films. Disclosed methods of improving these drawbacks include a method of reducing the number of retardation films (Japanese Laid-Open Patent Publication “Tokkai” No. hei 11-95208) and a method of using cholesteric liquid crystal layer (Japanese Laid-Open Patent Publication “Tokkai” No. 2003-15134, ditto “Tokkai” No. hei 11-95208). These methods were, however, still in need of bonding a plurality of films, and were insufficient in terms of thinning and cost reduction. Another problem resided in that light leakage from the polarizing plate in the oblique view in a black state could not completely be suppressed in the visible light region, and this consequently failed in fully improving the viewing angle. And it was also difficult to completely compensate the visible light, obliquely incident on the polarizing plate, over the entire wavelength of visible light thereof in a black state, and, consequently, color shifts depending on the viewing angle. A proposal has been made also on control of wavelength dispersion of retardation of the retardation film so as to reduce the light leakage (Japanese Laid-Open Patent Publication “Tokkai” No. 2002-221622), but this resulted in only an insufficient effect of reducing the light leakage. Still another problem was that influences given by changes in birefringence index of the liquid crystal layer were not fully considered, so that the device remained unsuccessful in obtaining a sufficient effect depending on birefringence of the liquid crystal layer.